He beat his wife once

His wife coaches jiu-jitsu. He participates, and he asks not to be consulted for jiu-jitsu advice, since he is not a coach. They roll together, which brings up the one rule worth passing along: if you can beat your spouse, don't. It isn't worth it.

He has beaten her exactly once, in a consensual jiu-jitsu exchange. The visual of their eye contact in that moment should have told him the potential long-term consequences before he finished the submission. He didn't read it in time.

His advice for anyone who trains with a significant other is to let him be the test subject. Just drill. Let them take the dominant position, and if they beat you, great.